Generally, when a plumber finds skulls in your backyard, it’s not a good sign.

Thankfully for one Floridan family, the discovery wasn’t a sign of foul play but the start of an 800-year-old mystery.

In early January, two mysterious skulls were unearthed in the backyard of house in Winter Garden, Fla., during the installation of a new pool. To everyone’s astonishment, the bones date back as far as 1200 A.D. and hark from South America.

According to ABC News, authorities were immediately alerted because human tissue was found on one of the skulls. Upon further examination, the cranium – which was believed to come from a young child around the age of 10 – was found to be hundreds of years old, its tissue mummified. The second skull is believed to have come from an adult male.

There’s also another bizarre twist: both skulls were found to have an “Inca bone” — a genetically distinct interparietal bone that indicates their owners were members of the Inca civilization in Peru. Archaeologists and examiners are puzzled over how they ended up in Florida, amidst some dirty pottery shards and a buried newspaper clipping from 1978.

“Back in the 1930s or 1940s, people would go on vacation and buy things like that, and maybe they buried them when they didn’t want them anymore. Another possibility is that it used to be a migrant farm worker camp, and some cultures will bring part of their heritage with them when they leave. It could be that they were moving on and decided to bury it there,” medical examiner Jan Garavaglia told the television news network.

“The mystery is how they ended up there,” Garavaglia summed up. “We don’t have any way of finding out.”

Erica Ho was previously a reporter for TIME in Hong Kong where she wrote about technology, pop culture and Asian international affairs. Before that, she worked at Gizmodo, Lifehacker and AOL. She now currently runs Map Happy, a travel-oriented site.